Indicating plug fuse



Dec. 19, 1933. F Q LA MAR 4INDICA'LIrm PLUG FUSE Filed March 17, 1952 Anvalluq nu MWWWMQ .3

3% )E fr i Patented Dec.'y `19', 1933 UNITEDTsai-'ivres' 1,940,627 f l l INDICATING PLUG FUSE Frank C. LaMar, New York, .N. Y., assignor to Great Western Fuse Company, New York, N. Y., afcorporation of Delaware v *Application March 17, 1932. "Serial No. 599,371 3 claim. (ci. zoo- 121i4 This invention relates to electrical devices, particularly to thermal fuses for use in connection with electrical circuits, of the Iform commonly known as aV plug fuse, combined with f jo means for indicating the integrity of the fusibley element, and more especially to means for pre` venting a willful'misuse of such a combined device.y

It is quite universally known vthat it isl necesk `11', sary to protect electrical circuits by means of devices, such as thermal fuseswhich` melt l or become disintegrated'or destroyed when an excessive flow of current passes through vthe circuit ofwhich thefuse formsa part. An espe- `l5 cially well known form of A,thermal fuse is that known as plug fuses. `Ordinary' plugV fuses consist, generally, of an insulating body having two terminals on the outside thereof yso constructedand arrangedv as to be readily brought 20 in contact with the terminals of an electrical circuit, by way` of what is known usually as a fuse block. These fusesare so universally used, and are made by so many different manufacturers,

and must all be usable in practically any of the well known forms of fuse block, that they have become, in truth, standard, so that they may well bereferred to as, standard, fuse plugs. At any rate, they .are substantiallyxstandard Aas `regardstheir general external dimensions,

Various forms of plug fuses have been made especially for lthe purpose lof enabling one to readily ascertain whether or not theffusible or thermal relement is intact. A desirable form for thus ascertaining the integrity ofthe fusible element is shown,-described and claimed'in my co-V pending application ySerial No.vk 594,02@V led February 19,1932, and entitled, Indlcating plug fuse.

The combined plug fuse and fusible element integrity indicator of my prior application, above mentioned, includes two spaced readily accessible,

electrical contacts which if bridged by an electrical conductor, which may readily beA done, would then not properly protect the electric circuit in which the plug fuse is inserted.

A principal object of this invention is to pro-A videa combined fuse and fuse integrity indicator, preferably substantially embodying the in-i bodiment selected Y to illustrate the` invention progresses, `and the novel features will be par` ticularly pointed out in the appended claims.v n

lIn describing the invention in detail and the particular physical embodiment selected t illus, 6o`

ytrate the invention, reference will be had to the accompanying drawing and the several views thereon, inv which'likev characters of reference designate like partsl throughout the several views, andinwhich: 'V Y' Figure lisa cross-sectional view of a com`` bined plug fuse and fusible element integrity lindicator with a structure embodying my invention included therein; Fig. 2 is a cross-sectional view of the device as shown by Figfl but taken on 7o` a plane at alright an'gle'to the'planeupon which Figure l is taken; Fig. 3 is a side elevational view of the devicev of Fig. 1'; Fig. 4 is a topplan viewv of the' device `asshown by Fig. 3; Fig. 5 is atop plan view of the'device as shown by Fig. 3 but'f with the cover portion of the rindicator removed; Fig. 6 is a` top plan view of the device as shown by Fig. 3 but with the integrity indicator removed. Y The device includes a body 1` formed of insulating, material, preferably a material such as porcelain. The body has an end contact member 2 having lan extension 3 projecting into the interior hollow portion 4 of thebody. The body is provided with an outer threaded shell contact 5 forming theother side ofthe electrical circuit. The contact k2 is connected withthe shell 5 by meansof a thermal fusible element 6. A` device Q embodying the abve `mentioned parts would be "substantially what is known as a plug fuse and would protect a circuit in whichit'is inserted if 90` ',shell'5 Wereconnected to one terminal of the circuit andcontact 2 to the other terminal. y

In order to indicate the integrity of the thermal fusible element 6, applicant provides a contacting portionor prong receiving clip contact# intermediate `the member 3 and the shell 5 and places an additional conducting member in contact with the member 3 leading to the prong receiving or contacting clip member 9. By connecting a lamp across the clips or contact members, as 7 and 9, an indicator for the memberv 6 is produced. In the form shown -by applicant, a lamp 10, preferably of a distinctive color indication such as a neon discharge lamp is positioned in a hollow insulating casing A11 having the top member or cover 12 formed with light apertures 13'. One terminal 14 of the lamp is connected to a conducting metallic prong 15 vand the other terminal 16 of the lamp is con nected througharesistance 17, preferably of the 110 grid leak type, to another conducting metallic prong 18.

If the prongs 15 and 18 are inserted into the clips '7 and 9, the lamp 10 is connected across the terminals of the fusible element 6. Just so long as the fusible element 6 is intact. sufficient current will not pass through the lamp 10 to cause it to light suiiiciently so as to be seen, but if the fusible element becomes disintegrated or blown, then the prongs 15 and 18 being connected from the shell 5 to the contact 2, sufiicient i current will pass through such circuit to cause the lamp to glow or light indicating the disruption of the fusible element 6.

The indicating portion of the device may be entirely removed from the body 1 by a pull upon the body 11. When this has been done, the clips or contact members 7 and 9 are in an exposed or partially exposed condition so that one might willfully place a conducting member in contact with clips 7 and 9 so that the fuse 6, evenif in place, would not function as intended, and if the fusible element k6 had been blown, then the effect of the opening of the circuit would be destroyed because the conductor connecting clips 7 and 9 would directly connect contact 2 with the shell 5. l

In order to prevent a dangerous condition which might arise by reason of placing an electrical conductor from the clip I to the clip 9, applicant has formed the member 8 as a fusible element. In order to indicate this, applicant has indicated a reduced portion 19, best shown in Fig. 2. This reduced portion 19 is formed of such material and is of such current carrying capacity that if current flows through it in excess of a very small amount, say a slightly greater amount than is necessary .to light the lamp 10, then the portion 19 melts and breaks the circuit.

By the use of the supplementary fusible element 19 applicant eifectually prevents a dangerous misuse of the plug portion of his combined plug and fuse integrity indicator, because if the fusible element 6 is destroyed and a ,jumper or electrical conductor is connected to and between clips 'l and 9, then upon the passage of the slightest amount of current, that is, a fraction of an ampere, the fusible element 19 included in the member 8 will be destroyed. Of course, the fusing value of the member 19 may be made almost anything desired, the limiting value, of course, being always somewhat higher than the current required to operate the indicator.

In order to separate and protect elements 6 and 8 from undesirably affecting one another, applicant uses the-sleeve 20, formed preferably of substantially non-combustible material, such as porcelain. f

Although I have particularly described one particular physical embodiment of my invention, and explained the principle, mode of constructionand operation thereof, nevertheless, I desire to have it understood that the form selected is merely illustrative, but does not exhaust the possible physical embodiments of the idea of means underlying my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

l. In a plug fuse, in combination: an insulating body; two metallic terminals on the outside of the body adapted for cooperation with the terminals of an electrical circuit to be protected; a thermal element connecting said two first mentioned terminals, two metallic contacts, one electrieally connected to one of the first mentioned terminals and adapted to be connected to one erminal of an electrical indicating device, and the other of the two metallic contacts connected to the other of the said iirst mentioned terminals and` including a fusible section ,of relatively low current carrying capacity, and adapted to be connected with another terminal of an electrical indicating device whereby an electrical connection between the said two metallic contacts will allow only substantially the current needed for the electrical indicating device to operate and a substantially greater current will cause the fusible section to fuse.

2. I" a system of electrical circuits wherein a plug fuse is used for protection against an excessive dow ci current, the combination of additional metallic contacts, electrically connected, one to each terminal of the plug fuse, said contacts adapted for connection to the terminals of a fuse integrity indicating lamp, the inclusion in the circuit of one of the said additional metallic contacts of a fusible section of relatively low current carrying capacity, whereby connection of substantial current carrying capacity between the additional metallic contacts will allow a current of suflicient value to flow and cause the said fusible section to become fused.

3. In a plug fuse, in combination: an insulating hollow body; two terminals on the outside of the body for cooperation with terminals of an electrical circuit to be connected; two conducting members, each connected electrically to one of the terminals, and one including a section of rela-tively low current carrying capacity; a thermal element of relatively high current carrying capacity connecting said two terminals; said conducting members forming contact terminals for cooperation with the contact terminals of a thermal element integrity indicator.

FRANK C. LA MAR. Y 

